Driving mechanism for sound recording and reproducing systems



Jufly 31, 1934. 1.. A. ELMER 1,968,438

DRIVING MECHANISM FOR SOUND RECORDING AND REPRODUGI NG SYSTEMS FiledApril 30, 1952 FIG.

lNl/ENTOR L. A. E LMER ATTORNEY Patented July 31, 1934 ATENT OFFICEDRIVING MECHANISM FOR SOUND RECOBD- ING AND REPRODUCING SYSTEMS Lloyd A.Elmer, West Orange, N. 'J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationApril 30, 1932, Serial No. 608,389

- 7Claims."(0l.2712.3)

This invention relates to sound picture apparatus and more particularlyto a driving and a control mechanism for maintaining a film at constantvelocity for sound translation.

55 In mechanism of this general character, a 'variety ofirregularitiesexist in the driving mechanism for the film. A majority ofthese irregularities are produced by infinitesimal imperfections in theparts of the driving mechanism and W in thefilm. These imperfections,however, need not necessarilybe great toaflect sound translation.Irregularities may be grouped into high and low frequency oscillationscaused by angular velocity variations. The high frequency irregularitiesare caused bygear teeth and consequent harmonics produced thereby. Thelow frequency irregularities are caused by cyclic modulations in speeddue to imperfections in the driving motor, imperfect layout of gearteeth, film variations and W other eccentricities.-

In order to obtain constant film velocity at the point of soundtranslation, 2. flywheel or terminating resistance is ordinarily coupledwith an elastic member to absorb velocity variations due toirregularities in the film and driving mechanism. Since, the manufactureof mechanism of this character cannot be accomplished in a manner tocompletely eliminate certain inequalities it follows that theinequalities in one assembly of mechanisms are-often difierent than inanother.

In consequence of this a diiference in the absorbing qualities of theelastic member maybe required for each assembly of. such mechanism inorder that it perfectly absorb velocity variations.

The object of this invention is, therefore, to provide a resilientcoupling or elasticity between the driving mechanism and the filmdriving cylinder which may be adjusted to obtain the cor- 40 rectdamping for absorbing driving mechanism reproducing device driven by anelectric motor.

The motor drives the mechanism of sound picture apparatus which includesthe intermittent motion and a'sprocket for regulating movement of thefilm. The aforementioned sprocket regulates the movement of the filmpast the point of 'sound translation and'the rotation thereof must bemaintained uniform at all times toprevent distortion of sounds. Forconvenience this sprocket will be hereinafter known as the sound,sprocket. A flywheel is mounted on the sound sprocket shaft to absorband give forth energy as required. This flywheel in itself absorbs filmload variations. A resilient or elastic member is placed between thedriving motor and the shaft on which the sound sprocket is mounted. Thisresilient member is used to absorb driving mechanism velocityvariations. A compound resilient member is used for this device, oneunit being approximately a fixed elasticity and a second unit ofadjustable elasticity The unit of fixed elastlcv ity comprises aplurality of springs connected between a member rotated by the motor anda hub member rigidly attached to the shaft on which the sprocket ismounted. The second member comprises a cylinder made of felt or othersuitable material placed between a member rotated by the motor and theflywheel. Means areprovided for adjusting the density of the feltcylinder and thus for adjusting the absorbing qualities of theelasticity as a whole. This adjustment alters the internal resistance ofthe felt cylinder and alters its torsibility. Ordinarily this adjustmentis made to obtain critical damping. Critical damping may be defined asthat which causes a mass which has been forced from its normal positionto return to its normal position in a minimum time and cause said massto stop, at said normal position, that is, not to override the normalposition. In some cases less or more than critical damping may bedesired depending upon the kind of oscillation or vibration to beabsorbed.

' In the consideration of this problem the constant or uniform velocityof the sound -sprocket must be taken as a zero factor. The uniformvelocity may be defined as that which would be obtained if noirregularities existed to introduce velocity changes. Thus in thedevices of this invention velocity changes only are of interest. Thesevelocity changes are of various frequencies depending upon the cyclicvelocity of the member producing the change.- A number of. driving linkscomprising shafts and gears are of necessity introduced between themotor and the driven end of the elastic or spring member. All of thosemechanisms of the sound picture apparatus including. the intermittentmotion are driven through the agency of these shafts and gears. Any ofthese devices including the motors, gears, shafts or driven mechanismsmay by slight imperfections cause velocity changes. The effect of thesevelocity changes is present in the elastic member in the form of angularvelocity/ changes. However, if this elastic member is properly adius ed,the velocity changes present in the elastic member are not transmittedto the sound sprocket in a degree which will cause sound distortions.

Fig. 1 is a view partly in cross section of the driving and drivenmechanisms and the elastic member; and

Fig. 2 is an elevation showing the arrangement of the springs for the.elastic member.

The driving motor, shaft, intermittent motion, etc., of the soundpicture apparatus is of conventional design and therefore has not beendisclosed. The shafting extending from the motor is connected to gear 8for driving the film past the point of sound translation. A portion ofshaft 7 has been shown on which the gear 8 is fastened by pin 9. Anelectric motor is ordinarily run at 20 revolutions per second, and isordinarily connected through a gear set to the various shafting forregulating the speed of different gears which drive individual units ofthe sound picture apparatus. Gear 8, for example, is ordinarily drivensix revolutions per second. Gear 8 is meshed with gear 10 and thus'anyirregularities in gear structure of either of these gears tend tointroduce velocity variations at a frequency of six cycles per second.Gear 10 is journaled on the sound sprocket shaft 6 and is connected byscrews 23 to the spring housing 11. The spring housing 11 is connectedthrough springs 13 to the flanged hub member 12. Flanged hub member 12is rigidly connected to shaft 6 by pin 16.

The manner of connecting the springs between housing 11 to the flangedhub 12 may be best understood by observing Fig. 2 in conjunction withthe disclosure of Fig. 1. Three studs 15 are screwed into the springhousing 11 for supporting one end of each spring. Studs 14 are screwedinto the flange of flanged hub 12 for supporting the alternate end ofeach spring. It will be noted that studs 15 extend through holes .1drilled at three points in the flange of flanged hub 12. When the soundpicture mechanism is at rest the studs 15 rest approximately as shownnear the metal surrounding the hole 41. When the mechanism of the motionpicture apparatus has been brought up to speed the stud 15 is brought tothe center of the hole as shown by the dotted stud 40. The shaft 6 isthus driven through springs 13 by gears a and 10. This comprises oneunit of the elastic member.

The sprocket 1 is rigidly connected to shaft 6 by nut 4 having a lockwasher 5 for holding nut 4 rigidly in position. The sprocket 1 is alsokeyed to the hub flange 12 by key 17. The flywheel 30 is rigidlyconnected to shaft 6 by screw 31, and locking stud 32. A recess 33 isformed in shaft 6 to receive the locking stud 32.

It will be noted that screw 23 extends through spring housing 11, gear10 and circular plate 24, rigidly fastening the three together. Betweenthe plate 24 and the flywheel a cylinder of felt is used as the secondunit of the elastic member. This cylinder of felt extends betweencircular plate 24 and circular plate 34. The circular plate 34 is heldin position by screw 35 which is arranged with a conical shaped end.Only one of the screws 35 has been shown in the drawing. There are,however, a plurality of such screws used. Normally three are all that isrequired. The felt cylinder is of such density that relative motionbetween the flywheel 30 and gear 10 causes twisting of the cylinder andthus tends to dissipate the energy of oscillations. To obtain the degreeof damping required inthe felt cylinder screws 35 are thrust into thecircular plate 34 until the felt cylinder is compressed to the properdegree of density. The internal resistance and torsibility of the feltcylinder are altered by this adjustment. The lock nuts 36 are thenfastened in place to retain the felt cylinder compressed to the properdegree for the correct damping of the particular mechanism of themachine in which the resilient coupling is used.

The compression of the felt cylinder by screws 35 as described has atendency to thrust gear 10 toward the flanged hub 12. To relievefriction between the gear and hub, a ball bearing comprising balls andraces 19, 20, 21 and 22 has been used. This is of particular value inpreventing the transmission of gear oscillations to the sound sprocketshaft 6.

From the foregoing it is apparent that the sound sprocket is driventhrough the composite elastic member comprising the springs 13 and thefelt cylinder 25 and that these two elastic members are interlocked witheach other. From this it is apparent that any adjustment of the densityof the felt cylinder controls the elasticity of the complete elasticmember to an extent that a particular quantity of damping may beobtained. The manner of judging the amount of damping required isordinarily obtained through the use of instruments for measuringvibrations and oscillations present in a given mechanism. By the use ofa compound elastic member as herein described the film 2 may be drivenat constant velocity past the point of sound translation which in thiscase is schematically shown by the rectangle 3. The apparatus for soundtranslation may be of any well known character.

The cylinder 25 has been described and is normally made of felt. It isnot, however, the intention of the inventor to limit himself to a givenmaterial for this cylinder since it may be manufactured of manyresilient materials capable of undergoing torsion and capable of beingcompressed to change its internal resistance and torsibility.

In some mechanisms a very small and light flywheel is used. In this casethe springs 13 are made extremely flexible to absorb oscillations and aparticular ofi-center adjustment of the spring studs must be-made. Thisbiasing or off-center adjustment is made by rotating the flywheelagainst spring tension before looking the flywheel in position on shaft6.

What is claimed is:

1. A drive for a continuous motion film having a sound record thereoncomprising a driving and a driven member, a resilient coupling mountedbetween said driving and driven member, said coupling having a member ofmaterial having internal resistance capable of undergoing torsion andcapable of being compressed to change its internal resistance andtorsibility and an adjusting means for compressing said material foraltering the internal resistance and torsibility of said member to varythe damping quality of said resilient coupling.

2. A drive for a continuous motion film having a sound record thereoncomprising a driving and a driven member, a resilient coupling mountedbetween said driving and driven member, said coupling having a cylinderof material having internal resistance capable of undergoing torsion andcapable of being compressed to change its torsibility and an adjustingmeans for compressing said material for altering the torsibility of saidcylinder to vary the damping quality of said resilient coupling.

3. A drive for a continuous motion film having a sound record thereoncomprising a driving and driven gear, a driven member for moving saidfilm, a resilient coupling mounted between said driven gear and drivenmember, said coupling comprising a set of springs and a cylinder ofmaterial capable of undergoing torsion and capable of being compressedto change its torsibility and an adjusting means for compressing saidmaterial for altering the torsibility of said cylinder to vary thedamping quality of said resilient coupling.

4. A drive for a continuous motion film having a sound record thereoncomprising a driving and driven gear, a shaft, a driven rotatable memberfor moving said film and a flywheel mounted rigidly on said shaft, acompound resilient coupling mounted between said driven gear and saiddriven member and flywheel, one unit of said coupling comprising linearelasticity in the form .of springs connected between said driven gearand said shaft, a second unit of said coupling comprising a cylinderconnected between said driven gear and flywheel of material capable ofundergoing torsion and capable of being compressed to change itstorsibility and an adjusting means for compressing said material foraltering the torsibility of said cylinder to vary the damping quality ofsaid resilient coupling.

5. A drive for a continuous motion film having a sound record thereoncomprising a cylinder for moving said film past a point of soundtranslation mounted rigidly on a drive shaft, a flywheel mounted rigidlyon said shaft, a driving gear in mesh with a driven gear, said drivengear being journaled on said shaft, 'a resilient coupling mountedbetween said driven gear and said flywheel, shaft and. cylindercomprising a set of spring connecting said driven gear and said shaftand a felt cylinder connecting said gear and flywheel and an adjustingmember for regulating the overall density of said felt cylinder to varythe damping quality of said resilient coupling.

6. A drive for a continuous motion film having a sound record thereoncomprising a driving and a driven member, a compound resilient couplingin the form of two resilient members in multiple between said drivingand driven member, one member being of fixed elasticity and the secondmember being of material having internal resistance capable ofundergoing torsion and capable of being compressed to change itsinternal resistance and torsibility and an adjusting means for alteringthe overall density of said second member thus altering the internalresistance and torsibility of said member to vary the damping of saidresilient coupling.

7. A drive for a continuous motion film having a sound record thereoncomprising a driving and driven gear, a shaft, a driven rotatable memberfor moving said film and a flywheel mounted rigidly on said shaft, acompound resilient coupling in the form of two resilient members inmultiple between said driven gear and said rotat- 139 able member, onemember of said coupling comprising linear elasticity in the form ofsprings connecting said driven gear and said shaft, a second member ofsaid coupling comprising a cylinder, connecting said driven gear andflywheel, of material capable of undergoing torsion and capable of beingcompressed to change its torsibility and an adjusting means for alteringthe overall density of said cylinder for altering its torsibility andvarying the damping of said resil- 113 ient coupling.

LLOYD A. ELMER.

